The present invention relates to an electroconductive plate-like titania and an electroconductive composition.
Electroconductive fillers to be incorporated into a binder such as resins include, for example, potassium titanate fibers and titania fibers which have been imparted electroconductivity by coating the surface of fibers with an electroconductive substance or by bringing about oxygen deficiency or the like due to reductive calcination. These fibers are practically used for antistatic effect, for shielding electromagnetic wave or for preparing electrodes as their raw materials because of their superiority in reinforcing property, dispersibility and electroconductivity.
In recent years, attempts have been made to develop fillers of improved electroconductivity which are capable of imparting the desired electroconductivity by use of a reduced amount of the filler. Among the attempts, a method comprising nitriding titanate fibers for converting part or all of fibers into titanium nitride is excellent because of ability to give high electroconductivity without impairing the fiber strength. More specifically, a method is known in which titania fibers or titania hydrate fibers are heated and reduced at 500 to 1000xc2x0 C. in a reductive atmosphere containing an ammonia gas to produce an electroconductive acid titanium nitride fibers (JP-A-215718/1989) and a method is also known in which potassium titanate fibers are heated and calcined in an atmosphere of an ammonia gas for producing potassium titanate fibers which are partly converted into titanium nitride (JP-B-27573/1993).
However, the fibers obtained by these methods have the following drawback. Because titanium nitride is exposed at part of fiber surface, the fibers are so hard that they easily wear a forming mold when used as a filler in a binder such as a resin. The electroconductive composition having a binder containing these fibers has the defect that it is inferior in slidability and resistance to wear. Further these methods pose the following problems. It is difficult to adjust the partial pressure of ammonia gas in the atmosphere and the electroconductivity is varied depending on the obtained fibers. Further, since reduction reaction proceeds in preference to nitriding reaction, the reaction requires a longer time in increasing the degree of nitriding, resulting in a likelihood of giving fibers which are collapsed in shape.
To overcome the foregoing problems of the prior art, the present inventor proposed titania fibers whose surfaces at least partly have titanium nitride coated with carbon (JP-A-228140/1999). The titania fibers containing carbon-coated titanium nitride are excellent in reinforcing property and electroconductivity such that the electroconductive composition having a binder containing these fibers is unlikely to wear the forming mold and have high slidability and wear resistance. Hence these fibers are desirable electroconductive fillers. Moreover, the fibers can be produced in a short time at a relatively low temperature. However, the titania fibers containing carbon-coated titanium nitride have a shape like, for example, the core of a propelling pencil, i.e. fibrous shape, which is about 5 to about 100 in average fiber length/average particle diameter (aspect ratio), and are oriented in a specific direction within the binder due to their fibrous shape and shows a characteristic of being different in electroconductivity and mechanical strength (especially mold shrinkage factor) between the values in the orientation direction and a direction vertical thereto.
This characteristic poses no problem when the fibers are used as a material for an electroconductive parts constituting electronic machines currently available.
However, the electroconductive parts constituting electronic machines require a higher and more uniform electroconductivity. Therefore, a further improvement is desired since the current technology is making a remarkable progress in the development of electronic machines of next generation.
On the other hand, plate-like graphite is known as a plate-like electroconductive filler. Nevertheless it is low in electroconductivity, and needs to be used in a large amount to give the desired degree of electroconductivity to the binder. This lowers the mechanical strength of the obtained composition.
An object of the present invention is to provide an electroconductive composition which enables the production of an electroconductive part which is not varied in electroconductivity and mechanical strength (especially mold shrinkage factor) according to the longitudinal or transverse direction of the part.
Another object of the invention is to provide an electroconductive composition which has higher and more uniform electroconductivity and which will not raise any problem when used as a material for electroconductive parts of next-generation electronic machines.
The present invention relates to an electroconductive plate-like titania containing at least 10% by weight of titanium nitride and at least 0.1% by weight of carbon component.
The invention further relates to an electroconductive composition containing the foregoing electroconductive plate-like titania and a binder.